As I posted before I am rebuilding a K301. the head was black with an excessive amount of carbon. I doubt it was ever cleaned. I tried to scrape it with a plastic scraper, didn't do much maybe removing 5% of the carbon. Then I used some hard wood (poplar) and it did even worse than the plastic. So much for following the directions. Then I tried a brass detail brush, I have no doubt that it would have removed all the carbon but it was also scratching the head so I stopped using it. I assume that more scratches and a rough surface would only give the carbon more to adhere to. Then I tried a piece of green scotch brite, it was even more aggressive than the brass brush and I was concerned about the corners around the valve area so i stopped with that. I then turned to solvents, paint thinner, acetone, carb cleaner....none of them did anythingThen came the purple power......The stuff is like magic. I plugged the spark plug hole with some plastic and poured some purple power in the head. I let it sit a few hours and when I went to check back in on it it turned from purple to black. A quick rubbing with my bare finger and dumped it out to reveal 90% of the remaining carbon was gone. I am currently resoaking it to get the last bit off, I cant believe how easy it is to do compared to the hour I spent with the plastic and wood scrappers that are suggested in the Kohler manual.